人们认为致癌作用是一个多阶段的过程,它通常包括癌的引发、肿瘤启动和恶性进展三个阶段。癌的引发阶段。多数甚至一切癌似乎是从单个干细胞的DNA突变“开始的”。这个干细胞就成为变异的致癌细胞。这个过程涉及对细胞繁殖循环和分化的失控。人们假定,这是作为在调节细胞增殖方面似乎起决定性作用的肿瘤抑制基因失活的结果而开始的。这些基因活动性的丧失,例如经由缺失或突变,能够导至细胞不受控制地生长。致癌作用的引发过程,也可能是原致癌基因转化的结果。这种原致癌基因 Carcinogenesis is thought to be a multi-stage process. It usually includes three stages: cancer initiation, tumor initiation, and malignant progression. The stage of cancer initiation. Most, if not all, cancers appear to be starting from DNA mutations in individual stem cells. This stem cell becomes a mutated cancer cell. This process involves the loss of control of cell cycle and differentiation. It is assumed that this started as a result of inactivation of tumor suppressor genes that appear to play a decisive role in regulating cell proliferation. Loss of these gene activities, such as through deletions or mutations, can lead to uncontrolled cell growth. The initiation of carcinogenesis may also be the result of transformation of proto-oncogenes. Proto-Oncogene